1. Field of the Invention
The present invention relates to a microwave plasma process apparatus. The apparatus enables etching of large-area substrates in super fine patterns at high speed. Further, the apparatus can be applied to oxidation, nitriding, doping, cleaning, cleaning ashing, and so on.
2. Related Background Art
The reactive ion etching (RIE) apparatus for applying RF (radio frequency) power between parallel plate electrodes opposed to each other is frequently used for pattern formation in fabrication of electronic components such as ultra-large-scale integrated (ULSI) circuits.
A conventional RIE apparatus is shown in FIG. 2. In a process chamber 201 there are provided a holder 203 for a substrate 202 to be processed, and a gas introducing means 204. An RF power supply 206 is connected to the holder 203. The process chamber is evacuated by an evacuation means 205.
Etching is carried out as follows. The inside of the process chamber 201 is evacuated to a vacuum through the evacuation means 205. Subsequently, etching gas is introduced at a predetermined flow rate through the gas introducing means 204 into the process chamber. Then a conductance valve (not shown) set in the evacuation means 205 is adjusted to keep the inside of the process chamber 201 at a predetermined pressure. Desired power is supplied from the RF power supply 206 to the substrate holder 203. Electrons are accelerated by an RF electric field to generate a plasma in the process chamber 201. The plasma ionizes the etching gas, and ions produced thereby are accelerated by a self-bias electric field formed near the substrate 202 to impinge upon the surface of the substrate, thereby etching the surface.
It is, however, not easy for the conventional RIE apparatus to achieve discharge under low pressures of about 10.sup.-3 Torr, under which anisotropy of ion incidence directions can be maintained, and therefore, the conventional RIE apparatus is not effective in performing anisotropic etching of fine patterns. With increase of integration of devices demand is increasing for further making the patterns finer, but the conventional apparatus fails to meet this demand.
Another etching apparatus under research, replacing the RIE apparatus, is a plasma process apparatus utilizing electron cyclotron resonance (ECR), which can achieve discharge under the low-pressure condition of about 10.sup.-3 Torr. The ECR is a phenomenon that in the case of the magnetic flux density of 87.5 mT, the electron cyclotron frequency of electrons rotating around magnetic lines of force is coincident with the ordinary frequency of microwave 2.45 GHz whereby the electrons resonantly absorb the microwave to be accelerated, thereby generating a high-density plasma.
An ECR etching apparatus is shown in FIG. 3. In a process chamber 301 there are provided a holder 303 for a substrate 302 to be processed, and a gas introducing means 304. An RF power supply 306 is connected to the holder 303. The process chamber is evacuated by an evacuation means 305. Further, in the process chamber the microwave is introduced through a microwave introducing window 307 and a magnetic field can be generated by a magnetic field generating means 308.
Etching is carried out as follows. The inside of the process chamber 301 is evacuated to a vacuum through the evacuation means 305. Subsequently, the etching gas is introduced at a predetermined flow rate through the gas introducing means 304 into the process chamber 301. Then a conductance valve (not shown) set in the evacuation means 305 is adjusted to keep the inside of the process chamber 301 at a predetermined pressure. The magnetic field of 875 G is generated in the process chamber 301 by the magnetic field generating means 308 and microwave power is introduced through the microwave introducing window 307 into the process chamber 301 to generate a plasma. Electrons helically move around magnetic lines of force, and when the frequency of rotation of the electrons comes to coincide with the frequency (normally 2.45 GHz) of the microwave (in the case of the magnetic flux density 875 G), the electrons resonantly absorb the microwave to be accelerated. Further, the electrons ionize neutral molecules by bombardment, thereby forming a high-density plasma. When desired power is supplied from the RF power supply 306 to the support holder 303 at this time, the ions are accelerated by the self-bias electric field formed near the substrate 302 to impinge upon the surface of the substrate, thereby etching the surface.
Use of such ECR etching apparatus permits discharge to occur even under the low-pressure condition of about 1 mTorr, which enables anisotropic etching of fine patterns.
The ECR etching apparatus as shown in FIG. 3, however, is not easy to generate a uniform magnetic field, so that the apparatus has a problem of nonuniformity of etching and a problem of device destruction due to charge separation in a direction along the surface of the substrate. Because of high temperatures of electrons, in the case of processing of fine patterns with high aspect ratios, abnormal etching (notch) is also likely to be caused by charge separation in a direction along the depth of the substrate.
An object of the present invention is to provide a plasma process apparatus and method, solving the problems in the conventional plasma process apparatus as described above, that can generate a uniform plasma in high density and in a large area even under the low-pressure condition of about 1 mTorr without using the magnetic field, thereby enabling etching of large-area substrates in super fine patterns and at high speed.